- server gate: the --allow-unauthenticated loopback allowance now requires
an actual plaintext connection (!gate_ctx->ssl), so a loopback TLS client
whose cert fails the --client-cn check is refused before any SCRAM
challenge instead of falling through the plaintext opt-in. Keep the
invalid-fd guard as belt-and-braces (unreachable after the policy check).
- test: rewrote test_wrong_client_cn_refused_before_auth_challenge to run
deterministically over 127.0.0.1 with --tls + --allow-unauthenticated and
a CA-valid wrong-CN client cert, asserting the gate refusal log and an
unchanged module tree (no skip).
- docs: --client-cn is mandatory with --tls; dummykey sidecar is secret
material; document all transient-fallback reasons; qualify
--allow-unauthenticated in README and --help so it cannot read as
permitting remote plaintext auth.
- credentials.h: drop stale restrictive-umask claim (fchmod forces exact
0600; only create/write/fsync/link/fchmod failure degrades to ephemeral).